Changes in the ratio of two separate toxin binding sites on the sodium channel protein during rat brain development.

The development of two separate toxin binding sites from sodium channels of rat brain was studied. Whereas [3H]saxitoxin binding developed gradually, reaching adult levels by 4.5 weeks after birth, the binding of [125I]scorpion toxin increased rapidly for the first 10 days after birth, then declined. The stoichiometric ratio of [3H]saxitoxin binding site to [125I]scorpion toxin binding sites changed during development from 0.5 in 8 day old rats to 1.9 in adult rats, implying separate biological regulation for each of these sites.